1. Field of the Invention
The present invention relates to a semiconductor device and a fabrication method thereof, and more particularly, to a power semiconductor module which has a metal terminal with a strengthened attachment to a conductive metal plate, a method of fabricating the metal terminal of the power semiconductor module, and a method of fabricating the power semiconductor module.
2. Description of the Related Art
Generally, a power semiconductor module is a structure including a power semiconductor chip mounted on a lead frame die pad, a conductive metal plate for heat radiation, and a package body formed of a molding resin such as an epoxy molding compound. A number of metal terminals that connect to a conductive metal plate or pattern on which the chip is attached are in the power semiconductor module. The metal terminals conduct electrical signals between the semiconductor chip and an external element to which the metal terminals connect.
FIG. 1 shows a conventional metal terminal 12 connected to a metal plate 10 of a conventional power semiconductor module. Metal terminal 12 includes a connection rod 12a and an attachment plate 12b. Attachment plate 12b has a flat surface that connects to metal plate 10, and connection rod 12a connects attachment plate 12b to an external element (not shown).
FIG. 2 shows the shape of an adhesive 14 after metal terminal 12 is attached to metal plate 10. In attaching metal terminal 12, adhesive 14 is coated on metal plate 10, and attachment plate 12b of metal terminal 12 is placed on adhesive 14. Then, a downward pressure applied to attachment plate 12b when attaching metal terminal 12 to metal plate 10. This downward pressure on attachment plate 12b can push adhesive 14 out of the interface between attachment plate 12b and metal plate 10. Accordingly, adhesive 14 attaches the side walls of attachment plate 12b to metal plate 10 but is lacking between attachment plate 12 and metal plate 10. The lack of adhesive 14 at the interface may reduce the adhesive strength between attachment plate 12b and metal plate 10, and thus a small external force may separate attachment plate 12b from metal plate 10.
In accordance with an aspect of the invention, a power semiconductor module including a metal terminal that maintains a strong attachment to a conductive metal plate. The metal terminal includes a hole and/or a protrusion in an attachment plate that attaches to the conductive metal plate. The hole increases the side wall area to which adhesive attaches and thereby increases the strength of the attachment. The protrusion, which is under the attachment plate, creates a gap or space for adhesive under the attachment plate and further increase the area of adhesive attachment and the bond strength.
In accordance with another aspect of the present invention, a method for fabricating a metal terminal for a power semiconductor module includes punching a hole in an attachment plate of the metal terminal. The punching typically creates the hole and a burr-shaped protrusion which extends from the bottom surface of the attachment plate of the terminal.
According to one embodiment of the invention, a power semiconductor module includes: a dielectric substrate and a conductive metal plate or pattern attached to the dielectric substrate; one or more semiconductor chips attached to the conductive metal plate or pattern; a metal wire connecting a pad of the semiconductor chip to the conductive metal plate; and a metal terminal including an attachment plate which contacts with a predetermined area of the conductive metal plate. The metal terminal has a hole in the attachment plate, overlying part of the conductive metal plate, and a connection rod which connects to the attachment plate to an external terminal. The attachment plate may further include a burrshaped protrusion formed around the edge of the hole on a surface placed in contact with the conductive metal plate. The metal terminal can be formed of copper or an alloy of copper and can be surface-treated to resist oxidation. The hole can have a circular, a rectangular, or other geometrical shape. Further, multiple holes can be provide in the attachment plate.
An adhesive surrounds the edge of the attachment plate, fills the gap between the attachment plate and the conductive metal plate, and fills the hole to thereby attach the metal terminal to the conductive metal plate
Typically, the power semiconductor module further includes: a heat sink attached to the bottom surface of the dielectric substrate; and an external vessel that attaches to the edge of the heat sink and protects devices within the module. The lower interior space of the external vessel can be filled with a gel-type soft resin, and the upper interior space can be filled with a hard resin.
In accordance with another embodiment of the invention, a method of fabricating a metal terminal includes: fabricating a metal terminal having an attachment plate for attachment to a conductive metal plate; and forming a hole through the attachment plate of the metal terminal by punching. The metal terminal can be surface-treated to prevent oxidation. Punching typically forms the hole. In particular, a punching machine pressing down on the attachment plate forms the hole with a surrounding protrusion below the attachment plate. The protrusion when in contact with a conductive plate creates a gap for adhesive between the attachment plate and the underlying conductive plate.
In accordance with another embodiment of the invention, a method of fabricating a power semiconductor module includes: fabricating a dielectric substrate onto which a conductive metal plate or pattern is attached; attaching one or more semiconductor chips to the conductive metal plate; bonding a metal wire to a pad of the semiconductor chip and a region of the conductive metal plate; mounting the dielectric substrate on a heat sink on which an adhesive is coated, and attaching the dielectric substrate to the heat sink by fusing the adhesive; attaching an attachment plate of a metal terminal to the conductive metal plate using an adhesive, the metal terminal having a connection rod and the attachment plate which has a hole formed through a surface to which the conductive metal plate is to be attached; attaching the edge of the heat sink to the external vessel using the adhesive; and filling the lower interior space of the external vessel with a gel-type soft resin, and filling the upper interior space of the external vessel with a hard resin.
Soldering can attach the metal terminal to the conductive metal plate, and an attaching jig is used to hold the metal terminal when the metal terminal is attached to the conductive metal plate.
According to an aspect of the present invention, a metal terminal can maintain a strong attachment to a conductive metal plate, and thus the reliability of a power semiconductor module is improved.